It is known for this kind of an electrophotographic image forming apparatus that several kinds of chemical substances are emitted during imaging operation. Typical chemical substances to be emitted (chemical emission) include ozone generated during charging of a photoconductor and toner powder dust generated during developing or fixing operation. Conventional solutions to the chemical emission include taking measures against the emission source of such chemical emission so as to decline the emission amount itself, and providing a filter to prevent emitted substances from being discharged outside from the apparatus. For example, in JP H5-150605 A, a divider plate is provided inside the apparatus to guide generated ozone to an ozonolysis device.
However, with a recent increase in awareness of global environmental conservation, ultra fine particles (with a particle size of 100 nm or less), which are substances different from ozone or toner powder dust, generated from electrophotographic image forming apparatuses have come to be seen as a problem. It has been unknown hitherto where such ultra fine particles are generated inside an image forming apparatus, and therefore it has been impossible to take effective measures for the problem. As a result, the ultra fine particles are considered to have caused contamination of the environment inside or around the apparatus.
As a result of the investigation conducted by the inventor of the present invention, it was found out that in an electrophotographic image forming apparatus, such ultra fine particles are mainly generated in a fixing device, more specifically in a rubber layer included in a fixing member (such as rollers and belts) which forms a nip section for fixing operation.
As shown in FIG. 15A, a general fixing member 300 includes three layers composed of a base material 301 made of a cylindrical core metal or an annular endless belt, a rubber layer 302 provided so as to cover the outer surface of the base material 301, and an outer layer 303 provided so as to cover the outer surface of the rubber layer 302. In this example, a heater 305 is provided in an internal space of the base material 301 for heating the fixing member 300 to a specified target temperature (a fixing temperature in the range of 180° C. to 200° C.). The rubber layer 302, which is made of a silicone rubber material, has heat tolerance to the fixing temperature and elasticity for allowing for the length of a nip section. The outer layer 303 is made of, for example, PFAs (tetrafluoro ethylene perfluoroalkyl vinyl ether copolymers) for aiding release of a sheet (recording material such as paper sheets) which passed the nip section. An end portion 302e of the rubber layer 302 and an end portion 303e of the outer layer 303 are both positioned inner than an end portion 301e of the base material 301 with respect to a direction along a central shaft C of the base material 301.
As a result of investigation conducted by the inventor of the present invention, it has been found out that as shown in FIG. 15B, when the base material 301, the rubber layer 302 and the like were heated with the heater 305 (reference sign H shows heat rays), siloxanes (designated by reference sign G) were generated in the form of ultra fine particles from the silicone rubber material which constitutes the rubber layer 302. Since the outer layer 303 made of PFAs and the like typically has a nature hard to transmit the ultra fine particles (gas barrier property), siloxanes G are emitted from the end portion 302e of the rubber layer 302. The emitted siloxanes G pollute the environment inside and around the image forming apparatus.
As a solution, simply covering and sealing the end portion 302e of the rubber layer 302 with the outer layer 303 may be contemplated. However, in the image forming apparatus, a fixing member is a component part having substantial increase and decrease in temperature. In the solution involving simple sealing, the rubber layer 302 and the outer layer 303 may be separated due to gas pressure of the ultra fine particles (e.g., siloxanes) generated from the rubber layer 302. If such a situation occurs, a performance of the fixing member and image forming apparatus will be degraded, leading to considerable reduction in their life span.